1. Field of the Invention
The present invention relates to a traveling test apparatus for a vehicle that establishes contact with a tread surface of a tire provided to a vehicle such as a car and measures a force received from the rotating tire and/or a circumferential velocity of the rotating tire.
2. Related Art
Conventionally, a traveling test apparatus for a vehicle, as described in Japanese Patent Provisional Publication No. HEI 6-18369, has been used in order to examine whether each of various traveling performances of a car satisfies a predetermined standard in a final inspection of a car manufacturing line or a car inspection. The traveling test apparatus includes a roller contacting with a tire provided to the car, a driving motor rotating the roller, and various sensors. The tire is driven by rotating the roller after setting the car such that the tire is placed on the roller. Various measurement values at the time when the tire is driven (e.g., a variation of a load and a circumferential velocity of the tire) are measured by the sensors. By carrying out tests using the above mechanism, test results which are substantially the same as those obtained through traveling on an actual road can be acquired even in a limited test space.
With such a test apparatus, a braking force measurement, force variation measurement, and speedometer test can be performed. Here, the braking force measurement is a test for checking whether a braking force of a foot brake or side brake of the car satisfies a predetermined standard. The force variation measurement is a test for measuring each force component generated while driving the car (6 component forces including component forces parallel to respective axes along a back-and-forth direction, right-and-left direction, and up-and-down direction, and moments of forces with respect to the respective axes). Further, the speedometer test is a test for verifying whether indication of a speedometer of the car shows an appropriate speed.
However, in such a conventional traveling test apparatus, what establishes contact with the tread surface of the tire is not a plane equivalent to a road surface but a circumferential surface of the roller. Accordingly, the tests using the conventional traveling test apparatus are not strictly equal to the traveling tests performed on the road.
Additionally, in the braking force measurement, it is required to rotate the tire with a low speed (approximately a circumferential velocity of 0.1 to 0.25 [km/h]) and relatively high torque. Meanwhile, in the speedometer test and force variation measurement, it is needed to rotate the tire with a high speed (approximately a circumferential velocity of 6 to 40 [km/h]). Therefore, in order to implement the speedometer test, force variation measurement, and braking force measurement with a single apparatus, it has been necessary to employ a motor that allows the tire to rotate with a high speed and high torque or a motor configured to be switchable between low-speed and high-torque driving and high-speed and low-torque driving. However, since such motors are expensive, a test apparatus for performing the braking force measurement and a test apparatus for performing the speedometer test and/or force variation measurement have separately been provided so far.
Further, conventionally, to measure the variation of the load transmitted from the tire to the roller, a load cell configured with a strain gauge being incorporated into an elastic body has been used. It is required for the braking force measurement, in which a high load has to be measured, to use a load cell with a measurement range of approximately 0 to 1000 [kgf]. Meanwhile, it is needed for the force variation measurement to measure a relatively small load of approximately 0 to 100 [kgf] more accurately. In general, an output of the load cell includes a measurement deviation of approximately 0.1 to 0.5 [%]. Thus, the measurement deviation of the load cell for the braking force measurement is approximately 1 to 5 [kgf], and it is impossible to accurately measure the force variation with the load cell for the above braking force measurement. For this reason, when the braking force measurement and force variation measurement are performed with the same apparatus, separate load cells have to be prepared for the braking force measurement and force variation measurement, respectively.